Decreasing feature sizes and increased aspect ratios on integrated circuits (IC) has led to the investigation of alternative methods of applying thin metal films to patterned surfaces for use as barrier layers, seed layers, gates, etc. Chemical fluid deposition (CFD) is one such technique that uses a supercritial fluid, usually CO2, as the solvent for metal precursors that are typically chemically reduced on a heated substrate in the presence of a dissolved reducing agent. This technique combines the process advantages of liquid and gaseous based metal depostion techniques and has been examined for use in various microelectronic applications. One of the potential problems observed with CFD is that the excellent transport and surface wetting properties of supercritical fluids lead to metal penetration into the dielectric film, especially with porous low k materials. This problem has also been observed to a lesser degree with CVD and ALD, two other methods for metal deposition. Metal penetration into the dielectric film raises the k value and can lead to open circuits, and so it is desired to devise a method that would prevent or reduce metal penetration by driving deposition on the low k surface.
Existing etch methods for low k films often result in damage due to radical attack on, or oxidation of, the dielectric film. Furthermore, post etch steps can include photoresist ashing processes that also attack the dielectric material. For CVD applied organosilicate glass (OSG) or spin on carbon doped oxide (CDO) films, this is usually observed as replacement of Si—O—C groups or Si—O—Si groups with polar Si—OH groups These hydrophilic substituents can lead to moisture absorption and elevated k values. It has been shown that treatment of such etch damaged films with hexamethyldisilazine (HMDS) or organochloro silanes can restore original k values by capping the Si—OH moiety with hydrophobic organic groups. These passivating treatments have been applied from both liquid solvents and supercritical CO2 (see, e.g., Toma and Schilling, U.S. Patent Application No. 20030198895).